Results and discussion

Physico-chemical properties of nutshells

To observe the microstructural features of the four different types of nutshells (NSs), Almond Shell (AS), Filbert Shell (FS), Pecan Shell (PS), and Walnut Shell (WS), SEM analyses were conducted on the inner surface, outer surface and the cross sections of the samples. The structure of nutshells reveals a substantial presence of porous tissue with a homogeneous distribution along the structural matrix. These porous tissues form perforations across the layers of the shell facilitating nutrient uptake by allowing the passage of liquids.[31,32] The ubiquitous distribution of these perforations throughout the shell structure is confirmed by SEM imaging shown in Figure 2 and Figure-S 3. Amongst these four NSs, Almond Shell (AS) and Walnut Shell (WS) exhibit remarkable uniformity in the distribution and arrangement of the apertures pattern, with AS demonstrating larger apertures than the WS. Diameter of these pores ranges from nano to micro scales, traversing both external and internal surfaces. Filbert Shell (FS), and Pecan Shell (PS) exhibit a disorganized distribution of pores (Figure 2 (d-i) ), ranging from nano to micro scales, facilitating the passage of fluids. Thus, the apertures of these four nutshells act as nano and micro channels for any fluid flow. The configurations of these micro/nanochannels have a variety of geometry including convergent, divergent, and parallel geometrics.[31-33]Moreover, the abundance of these perforations amplifies the adsorption capacity and augment the surface area for solid liquid interactions enabling faster capillary absorption of water. The composition of nutshells (NS) is primarily consisting of lignin, cellulose, and hemicellulose,[34,35] which are rich in hydroxyl groups, methoxyl, and carbonyl functional groups.[36] Therefore, NSs demonstrate mostly hydrophilic and negative surface charges.[37]